Fluorescence endoscopy utilizes differences in the fluorescence response of normal tissue and tissue suspicious for early cancer as a tool in the detection and localization of such cancer. The fluorescing compounds or fluorophores that are excited during fluorescence endoscopy may be exogenously applied photo-active drugs that accumulate preferentially in suspicious tissues, or they may be the endogenous fluorophores that are present in all tissue. In the latter case, the fluorescence from the tissue is typically referred to as autofluorescence or native fluorescence. Tissue autofluorescence is typically due to fluorophores with absorption bands in the UV and blue portion of the visible spectrum and emission bands in the green to red portions of the visible spectrum. In tissue suspicious for early cancer, the green portion of the autofluorescence spectrum is significantly suppressed. Fluorescence endoscopy that is based on tissue autofluorescence utilizes this spectral difference to distinguish normal from suspicious tissue.
A fluorescence endoscopy video system typically includes an endoscopic light source that is capable of operating in multiple modes to produce white light, reflectance light, fluorescence excitation light, or fluorescence excitation light with reference reflectance light, depending on particular filters inserted between the light source and the illuminated tissue, and between the tissue and the imaging sensor, respectively. A compact camera with the imaging sensor, such as a color CCD imager, can be disposed in the insertion portion (distal end or tip) of the endoscope; alternatively, the camera can be placed at the proximal end of the endoscope, in which case the acquired image can be transmitted from the distal end of the endoscope to the proximal end through a light guide.
Commonly assigned US Patent Application Serial No. 2006/0241496 A1 discloses a distal filter that can be placed over the distal end of a conventional white light imaging endoscope to allow the endoscope to perform fluorescence and white light examinations of a patient. The primary function of this filter is to prevent the transmission of blue light illumination used for fluorescence excitation and to transmit all other visible light over the field of view of the endoscope objective lens.
The filter may be mounted in a frame that is snap-fitted over the distal end face of an endoscope. The filter and/or frame may be secured to the endoscope with a mechanical, adhesive, magnetic force or other means.
Since fitting of the filter is performed in a clinical environment and for medical purposes, such fitting must be simple, accurate and reliable. In that regard, the small size of the filter represents a handling challenge. Even more challenging is the accuracy required for placing the filter over the video endoscope objective lens with sufficient precision. The tips of video endoscopes are typically 5-13 mm across and may include multiple closely spaced illumination ports, water ports, and one or more additional working channels, all sharing space with the objective lens.
Therefore, there is a need for a system and a method which enables accurate and reliable placement of an optical element, such as a filter, over the video endoscope objective lens in a clinical environment.